Black piedra and white piedra

Piedra, meaning stone in Spanish, is an asymptomatic fungal infection of the hair shaft, resulting in the formation of nodules of different hardness on the infected hair. The infection, also known as trichomycosis nodularis, is a superficial fungal infection arising from the pathogen being restricted to the stratum corneum, (the horny outer layer of the epidermis), with little or no tissue reaction. The conditions caused are considered superficial mycoses because the hosts do not produce any immunoreactive response.

The nodules are a concretion of hyphae (fungal filaments are known as hyphae) and fruiting bodies of the fungus, known as an ascostroma, from which the fungal spores are released. Fruiting bodies are aseptate ascospores that have a gelatinous sheath. Reproduction of the fungi is by the formation of endogenous ascospores, typically eight, in one ascus.

The source of infection is unknown and person-to-person transmission has been suggested, but this is not clear. Both sexes and people of all ages are equally affected. Two varieties of piedra may be seen; one called black piedra and one called white piedra.

The two types of piedra arise in different climatic regions. Black piedra occurs frequently in humid, wet tropical areas and is common in the central tropical areas of South America and South East Asia. Black piedra is typically caused by the fungi P. Hortae and Trichosporon ovoides. P. hortae is very common and has been found in the hairs of animals including primates, and in stagnant water, soil, and vegetables.

It has been suggested that for some native populations, black piedra may have cosmetic importance. There are records of women on some South Pacific islands sleeping with their hair buried in soil to actually encourage infection and development of black piedra. The nodular concretions of the fungal infection were regarded by some a quite attractive.

White piedra, caused by fungi in the Trichosporon genus, occurs in semitropical and temperate countries. Trichosporon genus is subdivided into six distinct human pathogenic species of which Trichosporon ovoides, Trichosporon inkin, Trichosporon mucoides, and Trichosporon asahii are linked to white piedra. Acremonium SP might also cause this infection.

The natural habitats of Trichosporon species are soil, lake water and plants, and such fungi are occasionally seen as normal flora of the human skin and mouth. Human white piedra can be contracted from animal hairs, including monkeys, horses and lower mammals. Colonization of human hair can be attributed to certain indigenous cultural habits like the practice of using plant oil in the hair by Brazilian Indians. Studies show that in the USA, occurrence of white piedra may be higher in African Americans than in Caucasians, though the reason for this is not clear.

Black piedra and white piedra clinical features

Both clinical varieties of piedra are mostly asymptomatic. However, according to the severity of the infection, progressive weakness of the hair shaft occurs causing the hair to be brittle.

Black piedra is a condition that is characterized by the presence of firmly adherent black, hard, gritty nodules, which are composed of a mass of fungus cells on the hair shaft, and cause disintegration and breaking of the hair. These stone-hard black nodules are usually localized to the scalp, but may also be seen on hairs of the beard, moustache and pubic hair, with the fungal activity limited to the cuticle. Black piedra is more frequent and less sporadic than white piedra, and the tiny nodules can be recognized by a metallic sound when brushing hair. Most commonly, the scalp hair is affected and nodules are present on the frontal, occipital and parietal scalp.

White piedra is characterized by white-to-tan nodules along the shafts of hair in the scalp, beard, eyebrows, eyelashes and groin, genital and perigenital areas. Numerous discrete soft nodules that are lightly pigmented are attached to the hair shaft and produce a gritty sensation when palpated. The nodules may be detached easily and the affected hairs may be split or broken. Genital white piedra can indicate a co-infection with corynebacteria. White piedra of the pubic hair seems to spread by sexual contact.

T. asahii and T. inkin can behave as opportunistic pathogens, particularly in immuno suppressed patients where they can have potentially life threatening consequences. In the immuno- compromised person, dissemination can take place, causing pruritic or necrotic cutaneous papules and nodules.

Black piedra and white piedra differential diagnosis

Clinically many hair disorders can be confused with piedra. Therefore, differential diagnosis, the process involved in distinguishing between two or more diseases and conditions with similar symptoms by systematic analysis of the clinical and diagnostic data, is essential, before arriving at a conclusive diagnosis and commencing therapy.
White and black piedra should be distinguished from each other. It can be noted that black piedra as compared to white piedra, presents a harder nodule that adheres to the hair shaft. Piedra can often be confused with pediculosis or lice infestation. Infections can co-exist with dermatophyte or candida infections, and erythrasma, a bacterial skin infection characterized by reddish brown, slightly raised patches, especially in the armpits and groin. White piedra should be differentiated from tinea capitis (a skin and hair follicle infection), and trichomycosis axillaris (an infection of the axillary and pubic hairs with the development of yellow, black, or red concretions around the hair shafts).

Black piedra and white piedra pathology

When there is a clinical suspicion of piedra, various diagnostic techniques are used to confirm the diagnosis. Hair can be sectioned and stained with toluidine blue. A 10-15% KOH solution can be used to prepare hair shaft nodules for staining on a glass slide. A fungal stain, such as chlorazol black E stain or Parker blue-black ink is added to delineate the hyphae.

Fungal cultures are performed on Sabouraud’s dextrose agar. Typically, fungal cells form a dense central mass around the hair shaft, and hyphae and spores make up the periphery of the nodule. The compact mass of pigmented hyphae and spores can be seen using light microscopy. Some Trichosporon species involved in white piedra (e.g. T ovoides) are inhibited by cycloheximide, and therefore do not grow in the dermatophyte test medium. Thus a lack of fungal growth in a test culture is not necessarily confirmation of an absence of infection.

Microscopic examinations of the nodules of black piedra reveal tightly packed, darkly pigmented hyphae, asci and ascospores attached to the hair shaft. They contain fruiting bodies. The periphery of the nodule has regularly aligned hyphae and arthoconidia (spores arising from pre-existing cells in the mycelium).

White piedra or infection with Trichosporon species when observed directly under the microscope shows that the nodules have darkly stained hyphae, blastoconidia (that reproduce by budding or fission) and arthroconidia fixed to the hair shaft. In some cases of white piedra, bacteria may co-exist, typically at the periphery of the nodules.

Black piedra and white piedra treatment

Shaving or clipping the infected hair is the best treatment for both types of piedra, but this is often not considered acceptable, particularly by women. Antifungal therapy may be initiated in conjunction with shaving. Black piedra may be treated with oral terbinafine, an anti fungal drug.

Effective therapies against white piedra include imidazoles, ciclopirox olamine, 2% selenium sulfide, 6% precipitated sulfur in petrolatum, chlorhexidine solution and Zinc pyrithione. Therapy with oral itraconazole (another anti fungal drug) for uncomplicated white piedra, which affects the scalp hair, may be good if topical remedies do not work. Genital white piedra remains a therapeutic challenge best addressed by combining shaving of pubic hair with use of a topical antifungal lotion.

Black piedra rarely recurs after treatment. White piedra is prone to sporadic recurrence and familial spread may also occur. The cause of transmission is not known, though there is suggestion of person-to-person transmission and transmission through animal contacts. If not correctly diagnosed and treated, black piedra may last for several years. It is suggested that people affected with black or white piedra can prevent spread of the infection by not sharing brushes, combs and other hair accessories.

Prognosis of piedra is positive because under normal circumstances it is a harmless disease. However, in immuno-compromised individuals there are associated risks as described above.

Black piedra and white piedra references